post_proc: complete reverb environmental interfaces

offload reverb effect leaves reverb delay, reflections level/delay and
properties as stub. Complete the implementation of these stub reverb
environmental interfaces.

CRs-Fixed: 937407
Change-Id: Id0002ff6770b40b41bec18b70a63ef15c64fcee7
diff --git a/post_proc/reverb.h b/post_proc/reverb.h
index 1a5ca0d..3bdd9af 100644
--- a/post_proc/reverb.h
+++ b/post_proc/reverb.h
@@ -40,7 +40,7 @@
     uint32_t    reverbDelay;
     int16_t     diffusion;
     int16_t     density;
-} reverb_settings_t;
+}  __attribute__((packed)) reverb_settings_t;
 
 typedef struct reverb_context_s {
     effect_context_t common;